The present invention relates to a distance measuring laser apparatus for delayed time measurements. More specifically, the invention relates to an input circuit means for such a distance measuring apparatus. Such distance measuring laser devices operate by measuring the travel or delayed time of a light impulse emitted by a laser and received, after reflection, by a receiver. Two channels are provided in the system. One channel is the so-called reference channel for deriving a starting signal in response to the emission of light impulses by the laser transmitter. The starting signal does not involve any delay time. The second channel is the so-called measuring channel and provides a stop signal in response to the reflected light impulse following the above mentioned delay time.
Such measuring devices or systems are known in the art. Reference is made in this context to German Patent Publications (DOS) 2,315,815, (DAS) 2,315,816, and (DOS) 2,348,458. These systems measure distances in accordance with the principles employed in pulse delay radar systems. In these laser distance measuring devices the delay time or traveling time of a wave packet is evaluated as a measure of the distance between an observer and a target, for example, a reflecting body. Thus, the determination of the distance is accomplished by measuring the time interval between the time of emitting an impulse and the time of return of the light impulse reflected by the target. In this type of distance measuring it is necessary that the time interval of the emission of a pulse and its return after reflection is not larger than the sequence period of the pulses because otherwise there would be an ambiguity in the interpretation of the measured distances.
Thus, known devices with so-called diode receiver or rectifier circuits have the disadvantage that they require a special intensity control for eliminating the above mentioned time ambiguities or uncertainties. Such intensity control is necessary because the receiver slope or receiver sensitivity varies as a function of the received light intensity.